The functional magnetic resonance imaging (IMRI) technique based on the blood oxygen level dependent (BOLD) contrast is a well-established neuroimaging modality. It has been generally accepted that fMRI can make accurate spatial maps of widespread brain activity; however, it is not suitable for studying temporal aspects of brain activity at the time scale of neuronal events due to the characteristic of slow BOLD response. Recent development based on our preliminary study has revealed the possibility of using the dynamic BOLD response to detect fast neuronal interactions at the time scale of tens of milliseconds. The primary objectives of this grant proposal are: 1) to establish and improve the dynamic fMRI approach for probing fast neuronal interactions within the same activation site, as well as between different activation sites in neural sensory systems; and 2) to characterize and understand the quantitative relationships among dynamic BOLD responses, metabolic responses and the origins of neuronal interactions elevated by brain stimulation. The objectives will be accomplished through the specific aims:(i) to quantitatively conelate BOLD signals detected by fMRI and evoked electric potentials detected by EEG during brain activation; (ii) to validate the reliability of the fMRl approach for probing fast intracortical neuronal interactions; (iii) to investigate the feasibility of IMRI for probing fast intercortical neuronal interactions during single and multiple sensory stimulations; and (iv) to study the mechanism and the quantitative relationship of the temporal BOLD responses related to the origins of neuronal interactions (primary effect), the hemodynamic and metabolic responses (secondary effects) using the MRI and MRS techniques. The success of this proposal will verify (1) the major hypothesis that IMRI is capable not only for spatial mapping of neuronal activity but also for temporal characterization of fast neuronal interactions, and (2) the notion that the proposed dynamic IMRI approach will provide a robust and noninvasive tool for studying functional processing of neural network at physiological and pathological conditions.